PSA tail gas is normally burnt as fuel in the SMR furnace. The PSA tail gas has low calorific value. PSA tail gas typically contains inert components such as 45%-50% CO2. The efficiency of burning PSA tail gas is impacted by the presence of these inert gases, as these are rejected with the flue gas at 250 F-400 F. The heat required to heat up these inert gases in the tail gas from ambient conditions (80 F-110 F) to the flue gas temperature of 250 F-400 F is lost.
The heat energy in the process gas after the shift reactor is recovered by producing steam or preheating BFW. However, the heat below 250 F-300 F cannot be recovered due to limited BFW quantity that corresponds to the steam production. The process gas below 250 F-300 F is normally cooled by air or cooling water before it is processed further in the PSA. This low level waste heat can be used to heat the PSA tail gas. Higher level heat from flue gas or syngas can also be used to heat PSA gas, instead of steam production, thus reducing the amount of export steam.